The present invention relates to an illuminating device and a display device provided with the illuminating device.
Today, a liquid crystal display device is now being rapidly spread in portable phones and information terminals provided in computers and ATMs and used in many and various environments. This rapid spread of the liquid crystal display device and the use thereof in many and various environments have required a characteristic of controlling an angle of visual field of each of image display elements composing the display device. The conventional liquid crystal display device is made so that not only a viewer located in front of the display but also another viewer located around the display can recognize the contents appearing on the display. In order to protect personal information contained in the contents appearing on the display, therefore, it is preferable to make the visual field angle narrower so that only the viewer located in front of the display can recognize the contents appearing on the display. On the other hand, when two or more viewers watch the display device or one viewer watches the display elements in multiple directions as the viewer moves his or her point of view, it is preferable to make the visual field angle wider.
As to the portable phone, the display contents are recognized in front of the display almost at any time. Hence, the display device provided in a portable phone is being required to make the visual field angle narrower so that the necessary ray of light is emitted only in the front direction, thereby making the power consumption lower. On the other hand, today, the portable phone is commonly equipped with a digital cameral function and a TV receiving function. The use of these functions needs a wider visual field angle. Hence, the portable phone is required to have a function of switching a narrow visual field angle to a wide visual field angle or vice versa.
To make the visual field angle narrower, there has been proposed a film having light transmittance portions and light absorption portions patterned at a certain period. (Refer to the documents Reissued U.S. Pat. No. Re. 27,617, JP-A-6-504627.) Concretely, a pattern period width of each combination of the light transmittance portion and the light absorption portion and a film thickness serve to shade a ray of light entered at a more angle than the geometrically defined angle. This makes it possible to restrict the visual field angle. The use of this type of film needs to paste or remove the film in order to switch an operation at a wide visual field angle to an operation at a narrow visual field angle or vice versa.
Practically, hence, the visual field angle characteristics, the wide angle or the narrow angle, cannot be arbitrarily used.
As another idea, there has been proposed a system of separately providing a liquid crystal panel for controlling the visual field angle and thereby switching one visual field angle to another by an electric operation. (For example, refer to the document JP-A-5-108023.) The fundamental principle of this system is analogous to that of the foregoing film-pasted liquid crystal display device. That is, the light transmittance portion and the light absorption portion are obtained by adjusting the orientation of liquid crystal molecules.
As described above, any conventional illuminating device is made so as to shade and absorb a ray of light in an area of a wide visual field angle when it is operated at a narrow visual field angle. Hence, the conventional illuminating device has a shortcoming that when it is operated at a narrow visual field angle, the luminance of the display is made lower than the luminance thereof when it is operated at a wide visual field angle. Further, when operated at a narrow visual field angle, in order to secure the same luminance of the display given when operated at a wide visual field angle in consideration of the reduction of the luminance, disadvantageously, the power consumption of the illuminating device is increased.